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1. Field of the Invention
The present invention relates to an improved method and apparatus for cooking starch that is to be used in a commercial laundry application. Even more particularly, the present invention relates to an improved commercial starch cooking method and apparatus wherein a recirculating flow line reticulates the cooking starch solution through a recirculating pump at velocities of flow not previously achieved in starch cooking apparatus which promotes a more uniform heating of the starch batch and breaks up lumps in the starch. In the preferred embodiment of the invention, the starch is caused to exit the cooker at high velocity through a strainer in the form of a standpipe in the bottom center of the cooker vessel by a high velocity centrifugal circulating pump which discharges back into the vessel through a spray nozzle adjacent the periphery of the vessel thereby establishing a high velocity circulation of fluid in the vessel causing a vortex to be exhibited around the discharge standpipe to continually mix and homogenize the starch, and clean the vessel wall.
2. General Background of the Invention
During the cooking of starch two phenomena take place. Naturally occurring starch granules undergo considerable physical change, usually xe2x80x9cswelling,xe2x80x9d until they are complete disintegrated, and the starch molecules are hydrolyzed into smaller particles. The resulting modified starch material depends upon processing conditions that are very important in determining the physical characteristics of the final starch solution. The swelling or hydrolyzed modification of starch, if precisely controlled, allows starch to be useful as a size or adhesive.
A compact cooker, reliably and consistently operable by a relatively unsophisticated individual, would be desirable. At a minimum, the cooker should bring the water and starch charge to a workable temperature and maintain the mix in a status for dispensing into the laundry apparatus. For effective starching of clothing, it is essential that the starch be a homogenous mix of water and starch, that is, without lumps or other concentrations of starch which present an uneven texture or appearance to the fabric of the washed and starched garment. It is customary in xe2x80x9ccooking starchxe2x80x9d for laundry purposes to utilize temperatures in the 165xc2x0 Fahrenheit thru 190xc2x0 Fahrenheit range (preferably between 180xc2x0 F. to 190xc2x0 F.). At higher temperatures, i.e., above 212xc2x0 F., the chemical and physical make up of the starch continues to change in such that the starch molecules begin to swell causing the volume of slurry to increase. As temperatures continue to rise, the starch molecules xe2x80x9cburstxe2x80x9d and the starch slurry no longer has the desirable properties as a sizing or adhesive.
The cooker must repeatedly perform the fill, cook and empty tasks with precision and regularity inherent in the design and operation of the machine and thus, without say sort of individual monitoring of the progress of the cooking procedure.
Several patents have issued for starch cooking devices. Some of the suggested patented systems require the use of a tank float device (e.g., U.S. Pat. No. 5,437,169 to Mitchell) to open and close the water supply valve via a solenoid. The float is immersed or partially immersed in the aqueous slurry of starch. Immersed operating components in starch solutions are a source of operating trouble. If the float becomes coated with starch, it fails to function, and presents overflow risks.
Some existing starch cookers (e.g., U.S. Pat. No. 5,437,169 to Mitchell; U.S. Pat. No. 2,730,468 to F. H. Martin; and U.S. Pat. No. 1,418,320 to E. W. Miller) use direct steam injection both to cook the starch and to agitate the starch solution. Existing cookers that use steam both to agitate and to cook often create starch solutions having lumps. It is believed that the concentrated heat of the steam directly on the starch solution causes localized heating and a temperature above that which the starch will remain stable as described above. These starch lumps cause uneven starching of the garments and a build up of starch on the press covers when the garments are pressed. Furthermore, direct steam induction results in sediment from within the boiler and or steam line to be mixed with the starch solution resulting in contamination (granular inclusions) and discoloration of the garments.
Other existing starch cookers (e.g., U.S. Pat. No. 5,437,169 to Mitchell, U.S. Pat. No. 2,940,876 to N. E. Elsas; and U.S. Pat. No. 2,516,884 to G. J. Kyame) use a plurality of valves to direct the contents of the containment tank either to the output conduit or the tank circulation. Problems have resulted from starch building up on such valves, including a failure of the valve to function.
Further problems with existing starch cookers involve the use of microprocessors to control a plurality of relays and process signals from various controlled communications. Microprocessors are particularly susceptible to heat and moisture, both of which are abundantly present in commercial laundries. When microprocessors are exposed to only minute amounts of moisture and/or heat they often cease to function. Thus, it would is desirable to provide a starch cooker which does not have the aforesaid susceptibility to heat and moisture.
Some large laundries use large vats of hot starch solutions and manually transfer hot starch from the vat to the washer. The manual transfer presents a danger of spillage and burning the operator. Another problem with this method is the large size of the vats and the consequently large quantities of starch. If the entire amount of starch is not used the same day it is prepared, the residual will frequently spoil and impart an unpleasant odor to the garments.
Other unsuccessful approaches at effective starch cookers are illustrated in U.S. Pat. No. 5,964,950 to Boling, the present inventor, wherein an external stand pipe is utilized to determine the fluid level within the vessel which, once the batch of starch is cooked and the slurry removed from the tank, residue of the slurry remains within the standpipe and creates an additional impediment to refill water rise in the pipe and erroneous readings occur. The patent also recites the inclusion of a gear pump for recirculating the slurry theorized to materially contribute to the break up of lumps. In operation, it has been found that the gear pump was only marginally effective in the breaking up of starch lumps and also exhibited a tendency to clog. In this previous cooker, it was theorized the use of a gear pump would blend the starch using the gears of the pump as a grinder. Through further operation, it has been found that with the use of gears, the starch revolved around the gears using the gears like paddles around the interior of the body when it was anticipated that the starch would be drawn through the center of the gears and therefore the meshing gear teeth would break up any lumps that had formed in the starch.
Through further evaluation it has been determined that the circulation of the starch with this particular prior art pump was approximately 3 gal per minute. When using straight water in the cook tank, prior to the adding starch, one would observe significant movement of the water in the tank. Once starch was added to this water, the movement due to the viscosity of the liquid slowed down considerably, more so than expected. The gear pump demonstrated the ability to pump on a free flow a maximum rate of 4 gal per minute with a liquid that was very thin such as water.
According to the present invention, the flow rate of the combined mix of starch and water, by using a centrifugal pump of about a ⅓ HP rating, with an inlet size of 1xe2x80x3 and an outlet size of xc2xexe2x80x3, which will pump on free flow about forty gallons per minute using a liquid such as water can provide the flow rate necessary for a thorough mix. Likewise, in the present invention, the inlet and outlet lines of the circulation pump are preferably copper and a minimum of xc2xexe2x80x3 in diameter. Additionally, an upright filter is installed on the interior floor of the cook tank, extending into the tank, to further assist in the break-up of starch lumps and continual mixing. The filter is also preferably made of copper and stands approximately 6 inches high from the bottom of a 5 gallon mixing tank, a relatively common size of starch cooker. It has been determined that the filter for the 5 gallon tank should contain approximately 30 holes of about xe2x85x9xe2x80x3 diameter over its surface to permit sufficient flow, yet break up any concentrations of starch. It has been discovered that with the inventive combination of vortex flow in the tank and the central filter, when water is being mixed into the tank that pump pulls the water off the center bottom of the tank through the filter and back through the side wall of the tank and across the heating coil with a flow of approximately 9 gallons per minute. This flow rate of the centrifugal pump together with the discharge of the heated mixture through the nozzle tangentially to the upper wall of the tank produces a strong vortex through to the center of the cook tank. It is preferable that the pump flow rate establish a vortex swirl around the internal perimeter of the tank with a depth that extends close to, but not below the top of the filter, i.e., such that the filter (and all of the holes) remains covered.
Once starch has been added to this tank, in a normal usage range of from one cup of starch per five gallons of water to 7 cups of starch per five gallons of water (the cup measure is by volume and not be weight) that the variance of mix and the viscosity of these mixtures made little change in the vortex in the center of the cook tank. All of the tests shown each test were in one-cup increasing increment of added starch and shows that there was little change in the depth or angular speed of the vortex in the center of the tank. The importance of this vortex serves many purposes in cooking starch. By radially circulating the starch from the center of the tank and it being drawn across the heating coil at higher rates of speed than conventional cookers, it keeps the heating coil clean, avoiding uneven heating that can occur if starch builds up on the coil. Reliable heating coil operation eliminates any need to subject the starch and water to direct steam injection, and thereby avoiding the troubles induced by such heating. The use of live steam injection not only causes deterioration of the starch water mixture, introduces boiler residue into the mix, but also may be hazardous to the operator. Therefore, it is significant improvement to enable the reliable and uniform heating of the starch by the inventive pumping of the mixture across the self-cleaning heating surface. In earlier such attempts of direct heating, the use of a coil in starch as a heat source failed because the coil did not experience a sufficient flow rate of the starch/water mixture over it and the coil would get coated with starch and the starch would act as an insulator and the coil would cease to transfer heat the starch mixture.
Another advantage of the vortex circulation is found in the effective way any lumps that may form in the starch mixture are pulled to and through the filter in the bottom center of the tank. Lumps are forcibly broken up and the starch dissolved, due to the circulation of the pump continually forcing the mixture past the pump impeller as well as by the draw of the stream through the filter, pulling the lumps through the many small holes in the filter. Also, with this aggressive circulation in a vortex fashion, the starch is now heated evenly throughout the tank without any cold spots. If cold spots are allowed to occur in a cook tank below 180 degrees, there is a danger that the mix will lose its homogeneity and xe2x80x9chighlightingxe2x80x9d could occur in the garments, resulting in light spots of improperly mixed and cooked starch.
With the selected centrifugal pump used being capable of pumping about forty gallons per minute on free flow, the pump may be adapted by putting approximately 40 lb. of head pressure from a reduced outlet pipe such that the pump the rate drops to 9 gallons per minute. Accordingly, this same pump may be used on smaller starch cookers, such as the described 5-gallon capacity as well as the larger starch cooker being of 14 gallons capacity. This may be accomplished by merely changing the line size from the tank to the pump inlet to change the flow of starch to properly size to the tank capacity. On both tanks a xc2xe inch size inlet is preferably used. On the smaller cookers, a xc2xd inch diameter size outlet is used (contrasted to the larger cooker using a xc2xe inch diameter size outlet. Tests of the smaller tanks show that by using xc2xd inch as an outlet size on the larger cooker that the gallons per minute drop to where the vortex is only slightly visible where on the smaller size cooker, the vortex is maintained relatively as with the larger outlet on the larger cooker. Once the line size had been properly sized for the volume in the tank the vortex was extremely strong and able to disperse any lumps that have appeared in the tank during the test. Once test was over and starch was drained there were no signs of any build up in the tank or on the filter.
On filling, it is common practice to allow water to fill in the tank approximately 6 inches so that starch will not lump or clump against the bottom of the tank due to the tank being hot or any hot starch that my have been left in the bottom of the tank between batches. During testing of the present invention, approximately 2 inches of hot starch was left in the bottom of the cook tank when the xe2x80x9cstartxe2x80x9d button was pressed for the new batch, and at the same time there was added a pre-measured amount of starch into the tank to increase the risk of lumps and during the cooking process. Surprisingly, there were no lumps or clumps visible after the tank was later emptied, due to the strength of the vortex and the capacity of the filter to remove theses lumps and clumps with the high velocity flow which creates the vortex.
Accordingly, the effect of using a centrifugal pump, an immersed heating coil, and a pump strainer, pulling the starch off the bottom center of the tank and injecting it across the coil to form a strong forceful vortex achieve the following:
Removal of lumps and clumps from a starch mixture
Mixing of starch uniformly without cold spots throughout the tank;
Heating the starch mixture, without any fear of exposure to an operator by using methods of
directs steam injection;
Heating starch quickly: by injecting the starch mixture across the coil, which keeps the coil
free of starch build up.
The present invention thus more quickly and completely cooks a quantity of starch solution required for multiple fills of starch cookers and expeditiously transfers a desired quantity of well cooked, smooth starch reliably to selected cookers than any in the prior art.
An object of the present invention is to provide a new and improved apparatus wherein starch solution may be thoroughly cooked without the liability of forming lumps or solid masses in such a manner to produce a complete homogeneous mixture.
Another object of the present invention is to provide a starch cooking and dispensing apparatus wherein the starch product may be maintained within close limits at the proper temperature for obtaining the best results as to penetration of the garments and the quality of sizing.
Another object of the present invention is to provide a starch cooking/dispensing apparatus that allows commercial laundries to use dry, or uncooked starch which is more economical than other forms of starch and nearly eliminates any waste of starch.
Another object of the present invention is to provide a starch cooking/dispensing apparatus that automatically transfers the hot starch solution directly into a commercial washer. This eliminates the dangerous practice of manual transfer and exposure to burns.
It is yet another object of the present invention to provide a starch cooking/dispensing apparatus that is self-cleaning. The present invention provides an improved apparatus for cooking a starch solution and then dispensing that cooked solution to a commercial laundry washer.
The apparatus includes a vessel with an interior surrounded by a wall for holding a volume of liquid.
A water supply inlet supplies water to the vessel interior for use in making the starch solution.
The vessel provides an open top into which dry starch can be added for making the starch solution.
A steam supply inlet is provided for adding steam to the vessel interior via a header that separates the steam from the solution so that the volume of liquid within the vessel can be heated.
A level controller controls the level of fluid within the vessel in between minimum and maximum fluid levels.
A recirculation flow line provides an inlet and an outlet that each communicate with the vessel interior. A pump mounted in the recirculation flow line pumps fluid from the inlet to the outlet during a recirculation of the fluid within the vessel interior.
In the preferred embodiment, the pump includes a geared impeller that breaks up starch lumps flowing in the recirculation flow line.
A discharge flow line is provided for transmitting the heated slurry of starch and water from the vessel interior to the laundry washer.
In the preferred embodiment, a discharge pump dispenses the heated solution of starch and water from the discharged flow line to the laundry washer, wherein the discharge pump has a geared portion that breaks up starch lumps flowing therethrough.